Reinforced films made from water soluble polymers

ABSTRACT

A dried film reinforced with coalescable water insoluble polymer particles which are substantially noncoalesced is disclosed. Also disclosed are dried films reinforced with noncoalesced water insoluble polymer particles which are readily water dispersible. Also disclosed are stable aqueous dispersions for formation of such films which comprise (a) a water insoluble component comprising coalescable polymer particles which have a T g  less than 55° C. and a majority of which have a particle size of less than 1 micron; and (b) a water soluble component which comprises a water soluble polymer capable of inhibiting coalescence of the polymer particles, or a water soluble polymer and a component capable of inhibiting coalescence of the polymer particles.

This is a divisional of U.S. application Ser. No. 07/810,646 filed Dec.19, 1991, and now U.S. Pat. No. 5,416,181, which is acontinuation-in-part of application Ser. No. 07/650,965 filed Feb. 5,1991, and now abandoned, which is a continuation-in-part of Ser. No.07/472,632 filed Feb. 5, 1990, which issued as U.S. Pat. No. 5,003,022on Mar. 26, 1991, which is a continuation-in-part of application Ser.No. 07/309,248 filed Feb. 10, 1989, and now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to reinforced films of water solublepolymers and stable polymeric dispersions which can be dried to producesuch films. Specifically, the invention relates to dried films of watersoluble polymers reinforced with noncoalesced water insoluble polymerparticles where the film comprises a water insoluble component and awater soluble component.

Starch is a water soluble film forming polymer but starch films are notused in many applications because they are brittle, generally low instrength, do not give substantial gloss in paper coatings, and arefrequently incompatible when mixed with other polymers. Although thebest starch films are thought to be formed by starch polymers havinghigh molecular weights and high concentrations of straight chainpolymers, such aqueous solutions of starches hav undesirably highviscosities (it being understood in the art that starch is a watersoluble polymer). Thus, to prepare strong starch films, very dilutestarch solutions are used, which require the removal of very largeamounts of water through an expensive drying operation.

One way to reduce the viscosity and increase the solids prior to filmformation is to thin the starch by hydrolyzing the starch polymerchains. Unfortunately, such thinning reduces the strength andflexibility of the resulting film. As the starch films are dried, thepolymer chains hydrogen bond to one another resulting in a great deal ofshrinkage. Shrinkage leads to the creation of stresses in the finishedfilm, which can distort, craze, curl, or crack the film. In addition,hydrogen bonding between starch molecules causes a phenomenon known as"retrogradation" or "setback." In this case, the chains can bondtogether so strongly that they will not redisperse, even in boilingwater. Other carbohydrate and noncarbohydrate film forming water solublepolymers suffer from many of these same problems. Various attempts havebeen made in the art to improve the propertie. of starch and other watersoluble films but most have provided only marginal improvements inproperties. One improvement of interest has been to increase the linearchain fraction of starch, which is amylose. While this has providedfilms with increased strength, the films have had limited utilitybecause of high cost, difficulty of dispersing the original high amylosestarch granules, and increased ease of retrogradation of the linearmolecules. To be useful, these films have required addition ofplasticizers or humectants. Again, other carbohydrate as well as manynoncarbohydrate water soluble film formers have similar difficulties.

Mixtures of starch or other water soluble polymers and latexes have beenused as film forming compositions for a long time. However, in thesecases, the films which are formed consist of regions of coalesced waterinsoluble latex polymer particles interspersed with domains rich in thehydrophilic water soluble polymer. It is believed that the formation ofa film from latex by coalescence involves a first step of water lossfollowed by association of the polymer particles ultimately followed byintermixture of polymer chains resulting in loss of the discreteparticle structure.

These films from mixtures of water soluble polymers and latexes arethought to consist primarily of a coalesced latex continuous phase,interspersed with regions or domains rich in the water soluble polymer.No effort is made to prevent the latex from coalescing. Indeed, effortsare made to encourage coalescence of the water insoluble polymerparticles because it is believed that such coalescence is necessary toform a continuous film having desirable properties including strength.

One area where such materials are used has been in paper coating. Inpaper coating applications starch is often blended with latex to formthe binder system which, when mixed with pigment, forms a basic coatingcolor. Unfortunately, films with coalesced polymer particles used asbinders in paper coating compositions tend to shrink. They also havegreatly reduced water dispersibility compared to water soluble polymers.Moreover, when latex particles coalesce to form a film, the resultingshrinkage can contribute to mottle-type defects which can be deleteriousto gloss. Coatings comprising starch alone as a binder are weak and tendto shrink, resulting in a rough surface having low gloss. Thus, thereexists a need in the art for aqueous dispersions having improved filmforming properties which can be used as binders in coating colorcompositions and other end uses.

SUMMARY OF THE INVENTION

The present invention relates to reinforced films including readilywater dispersible films and stable polymeric dispersions which can bedried to produce such films. Specifically, the invention relates tofilms comprising a water insoluble component and a water solublecomponent reinforced with water insoluble polymer particles, which,although coalescable, are substantially noncoalesced. Such films may bereadily redispersible in water but need not be. While not wishing to bebound by any theory of invention, it is believed that the substantialabsence of coalescence of the coalescable water insoluble particlesrenders the films readily redispersible assuming that no separateprovision has been made for crosslinking or insolubilization. Theinvention also provides stable aqueous dispersions capable of producingsuch reinforced films. The stable polymeric dispersions can compriseblends of water insoluble and water soluble components or the product ofa polymerization reaction of one or more unsaturated monomers carriedout in the presence of the water soluble components. Such reactionproducts include graft copolymers including starch graft copolymers. Theaqueous dispersions are characterized by the capability of forming whensubjected to atmospheric drying at about 70° F. a film reinforced withnoncoalesced water insoluble polymer particles. While it is possible tocoalesce the water insoluble polymer particles under other temperaturesand conditions, the dispersions of the invention can all form filmsreinforced with noncoalesced coalescable particles when dried at about70° F.

The aqueous polymeric dispersions and films provided by the inventionare characterized by unique properties which are valuable in coatingapplications generally and paper coating applications in particular.Specifically, films produced using the dispersions of the invention arecharacterized by high levels of strength and toughness. When thedispersions are used as binders in coating color compositions, highlevels of print gloss result. The films comprise a continuous phase ofwater-soluble-polymer reinforced with noncoalesced submicron sizedparticles which provide toughness and mechanical strength to the film.The noncoalesced particles also absorb shrinkage stresses and can thushelp provide a smooth continuous film surface.

In cases where readily water dispersible films are provided, theinvention provides dried powders capable of being convenientlyredispersed in water to form stable aqueous dispersions and methods ofpreparing and dispersing same. In addition, the invention providescoating color compositions comprising the aqueous dispersions of theinvention including coating color compositions comprising greater than60% solids by weight along with methods of coating substrates includingpaper and substrates coated thereby.

The dry, stable reaction products and blends of the invention provide avariety of advantages. Specifically, the products are capable of beingredispersible when added to water and will have substantially the samephysical properties including particle sizes after they are dried andredispersed as before they were initially dried. This leads to numerouscommercial advantages including the ability to make and store a dryproduct that later can be conveniently redispersed. The dryredispersible products can reduce the costs of shipping materials, suchas coating color binders, there being no water to ship. The inventionalso provides the ability to make and store a dry product for extendedperiods where that product might not have been capable of being storedas a stable liquid dispersion for the same period of time. The inventionalso provides the ability to rehydrate a dry material to a higher solidsconcentration than the solids concentration at which it was originallymade. Moreover, the dry product can be used directly as a dry materialin applications where a liquid could not be used. Alternatively, it canbe used dry in applications such as by adding it directly to an aqueousdispersion comprising a coating color pigment.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1a is a photograph of 100% enzyme thinned starch film;

FIG. 1b is a photograph of an enzyme thinned starch film including 3%latex by weight;

FIG. 1c is a photograph of an enzyme thinned starch film including 6%latex by weight;

FIG. 1d is a photograph of an enzyme thinned starch film including 12%latex by weight;

FIG. 1e is a photograph of an enzyme thinned starch film including 24%latex by weight;

FIG. 1f is a photograph of an enzyme thinned starch film including 30%latex by weight;

FIG. 1g is a photograph of an enzyme thinned starch film including 40%latex by weight;

FIG. 1h is a photograph of an enzyme thinned starch film including 60%latex by weight;

FIGS. 2a and 2b are photomicrographs depicting a dispersion of astyrene-butadiene/starch reaction product and its reconstituted product;

FIGS. 3a and 3b are photomicrographs depicting a dispersion comprising ablend of latex and starch and its reconstituted product;

FIG. 4a is a scanning electron micrograph of a latex film;

FIG. 4b is a scanning electron micrograph of a latex/starch blend film;

FIG. 4c is a scanning electron micrograph of a latex/enzyme thinnedstarch blend film; and

FIG. 4d is a scanning electron micrograph of a styrene/butadiene starchgraft copolymer film.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides compositions which greatly improve theproperties of films of starch and other water soluble film formingpolymers while avoiding the problems which arise in other attempts toimprove these properties. The present invention makes use of small waterinsoluble polymer particles to reinforce the hydrophilic continuousphase of water soluble polymers. This reinforcement by coalescable waterinsoluble particles gives beneficial properties to the films, such astoughness, tear resistance, and the like. In addition, thisreinforcement is particularly important in cases where low molecularweight water soluble polymers are required for higher applicationsolids. Additionally, the properties of films from higher molecularweight water soluble polymers can also benefit from this reinforcement.

Another surprising aspect of the present invention relates to theability to maintain noncoalesced sub-micron sized hydrophobic polymerparticles in a water-soluble-polymer film after drying. The irreversibleassociation of sub-micron sized water insoluble polymer particles upondrying is well known. As water is removed, the particles typically jointogether in a substantially irreversible manner, properly known in theart as coalescence, but sometimes referred to as coagulation,aggregation or agglomeration. As used herein, the term "coalescence"shall refer to the substantially irreversible combination of particlesinvolving deformation and merging of polymer chains across particleboundaries to create long range order. Most surprising, there is notendency for the coalescable polymer particles to coalesce even underrather severe conditions of drying at elevated temperatures.

The films of the invention comprise a unique structure wherein they arereinforced by coalescable water insoluble polymer particles which oftenare elastomeric and which, because they are noncoalesced and distributeduniformly throughout the film, provide toughness and mechanical strengthto the film. The films of the invention require the followingingredients: (1) small coalescable water insoluble polymer particlessuch as are prepared by emulsion polymerization; (2) one or more watersoluble polymers; and (3) a component capable of inhibiting coalescenceof the water insoluble polymer particles when that function is notprovided by the water soluble polymer(s). The dried films of theinvention can be produced from stable aqueous dispersions of theinvention by coating the dispersions on a surface and drying. Suchdispersions comprise a water insoluble component and a water solublecomponent wherein (a) the water insoluble component comprisescoalescable polymer particles which have a glass transition temperature(T_(g)) less than 55° C. and a majority of which have a particle size ofless than 1 micron; and (b) the water soluble component comprises awater soluble polymer, such as starch or a starch hydrolyzate, capableof inhibiting coalescence of the polymer particles, or a water solublepolymer and a component capable of inhibiting coalescence such as, butnot limited to, a polyol. The coalescable water insoluble particles ofthe dispersions comprise greater than 3% by weight of the solids. Thewater soluble component comprises greater than about 25% by weight ofsaid solids. The water soluble polymers can be film forming polymerssuch as starch, but can also be non-film formers which, nevertheless,form films when carrying out the invention. Nevertheless, when the watersoluble component is starch alone, the starch is a starch hydrolyzateproduct having an intrinsic viscosity of less than 0.12 dl/g.

The invention further can provide a dried powder capable of beingconveniently dispersed in water to form a stable aqueous dispersioncomprising a water insoluble component and a water soluble componentwherein the coalescable water insoluble particles comprise greater than3% by weight of the solids making up the dispersion while the watersoluble component makes up greater than about 25% by weight of saidsolids. Specifically, the water insoluble component comprisescoalescable polymer particles which have a T_(g) less than 55° C. with amajority of the particles having a particle size of less than 1 micron.The water soluble component comprises a water soluble polymer capable ofinhibiting coalescence of said polymer particles or a water solublepolymer and a component capable of inhibiting coalescence of saidpolymer particles. The dried redispersible powder of the invention canbe obtained by preparing the stable aqueous dispersions of the inventionand drying the dispersions under conditions selected to avoidcoalescence of the water insoluble polymer particles. The dispersionscan be dried by a variety of means because there is little tendency tocoalesce the particles even under extremes of temperature. Such dryingmeans include spray drying, drum drying and vacuum drying (includingfreeze drying) with spray drying and freeze drying being preferred.These dispersions can also be treated by selective solventprecipitation. In addition, dispersible powders can be prepared from theredispersible films of the invention by fragmenting the film. The driedpowders can be easily transported and can be redispersed in water whenan aqueous dispersion is desired.

The stable aqueous dispersions can be prepared by polymerization ofunsaturated monomer compounds in the presence of starch or other watersoluble polymer components to form a reaction product such as a starchgraft copolymer. Alternatively, the dispersions can be prepared bysimple blending or mixing of the water insoluble component comprisingcoalescable polymer particles with the water soluble component includinga water soluble polymer and optionally, if needed, a component capableof inhibiting coalescence. A variety of blending methods are possibleincluding (1) adding dry polymer particles to an aqueous dispersion ofthe water soluble component; (2) adding dry water soluble components toan aqueous dispersion of water insoluble polymer particles; (3)combining dry water insoluble polymer particles with a dry water solublecomponent and dispersing the dry components in water; and (4) combiningan aqueous dispersion of the water soluble component with an aqueousdispersion of the water insoluble polymer particles. The dry blendingtechniques advantageously allow preparation of dispersions having highsolids levels of 60% by weight or more.

According to an additional method, dry redispersible powders may beobtained by selective solvent precipitation. Specifically, an aqueousdispersion such as one containing a styrene/1,3-butadiene starch graftedcopolymer (Penford Products Co., Cedar Rapids, Iowa) PENGLOSS®, can beslowly added to a solvent such as isopropanol and be precipitated fromthe isopropanol and vacuum filtered. The precipitate can then be ovendried and subjected to ball milling to produce a light powder.

The invention also provides coating color compositions comprising apigment and a binder comprising the dispersion of the invention. Thecoating colors can also be prepared with high solids levels of 60%solids by weight or greater. The dry materials of the invention can, infact, be blended directly with a pigment such as clay in a make-downstep. The coating colors can be used to coat paper and other substratesby applying to the substrate and drying the coating. Papers coated usingthe binders of the invention exhibit increased ink gloss, stiffness,brightness and along with opacity, improved porosity and printingquality. These improved properties are believed to result from thereinforced structure provided by the invention.

Water Soluble Component

The water soluble component comprises a water soluble polymer capable ofinhibiting coalescence of the coalescable water insoluble polymerparticles or a water soluble polymer and a component capable ofinhibiting coalescence of the polymer particles. The water solublecomponent comprises from about 25% to about 97% of the solids content ofthe final composition. The water soluble component comprises at leastabout 25% of the total solids because that amount is believed to be theminimum required to allow the film of the invention to be formed.Preferably, the water soluble component comprises from 50% to 80% of thetotal solids content.

Water soluble polymers useful according to the invention are those whichcan form films. Suitable water soluble polymers include carbohydratessuch as starch derived from different plant sources, including highamylose and high amylopectin varieties. By "starch," as referred toherein, is also meant water soluble film forming polymeric materialsderived from starch including starch derivatives such as starchhydrolyzate products, modified starches, modified starch derivatives andmaltodextrins. Other water soluble polymers useful with the inventionare polyvinyl alcohol, cellulose derivatives, natural polysaccharidegums and their derivatives, polyethylene glycol, water soluble acrylics,water soluble polyesters, polyvinyl pyrrolidone, casein, gelatin,solubilized proteins, polyacrylamide, polyamines, polyquaternary amines,styrene maleic anhydride (SMA) resins, polyethylene amine and any watersoluble polymer. Particularly preferred are starch, starch derivativesthereof, modified starches and derivatives, thinned hydroxyalkylstarches, polyvinyl alcohol, cellulose derivatives, polysaccharide gums,polyethylene glycol and maltodextrin. Most preferred are modified starchderivatives and hydrolyzed starches.

One of the advantages provided by this invention is thatdepolymerization of the water soluble polymer may be carried out to gainthe advantage of high solids, low viscosity application and reducedshrinkage without giving up flexibility or strength in the reinforcedfilm. A particularly preferred material is a starch hydrolyzate productthinned such that it has an intrinsic viscosity of less than 0.12 dl/g.

Components Capable of Inhibiting Coalescence

In many cases, the water soluble polymer itself, or components therein,will prevent coalescence of the water insoluble polymer particles. Forexample, thinned starches including maltodextrins and particularlystarch hydrolyzate products having an intrinsic viscosity of less than0.12 dl/g can prevent coalescence of the water insoluble polymerparticles.

In other instances it may be necessary to add an additional material toprevent this coalescence of the water insoluble polymer particles in thewater soluble polymer film. Accordingly, a low or intermediate molecularweight component can be incorporated into the water soluble component toinhibit such coalescence. Suitable components include highly watersoluble and water miscible components including urea, low molecularweight polyvinyl pyrrolidone (PVP), amino acids and polyols, e.g.,glucose, sucrose, maltose, maltodextrins, glycerol, propanediol,sorbitol, pentaerythritol, cyclodextrins, polydextrose, polyvinylalcohol. Components capable of inhibiting coalescence can be mixed dryor in a liquid solution with dry or dispersed water soluble polymer, orin a mixture of the insoluble particles, or in a mixture of theinsoluble polymer particles and the water soluble polymer.Concentrations of 5% or 10% or more of components capable of inhibitingcoalescence are typical in practice of the invention but one of ordinaryskill in the art can readily determine the suitable concentration to beadded for a component given the type and proportions of the film formingpolymer and water insoluble component in any particular mixture.

Water Insoluble Components

The water insoluble components comprise coalescable water insolublepolymer particles and optionally comprise noncoalescable water insolublepolymer particles. For the purpose of this invention, a water insolublepolymer particle is considered "coalescable" if a film cast from suchpolymer particles dispersed in water requires a temperature no higherthan 85° C. to coalesce at atmospheric pressure. Particles areconsidered to coalesce if there is a substantially irreversiblecombination of particles involving deformation and merging of polymerchains across particle boundaries to create long range order. Inaddition to the coalescable polymer particles, the water insolublecomponents can also optionally comprise noncoalescable water insolublepolymer particles that will not coalesce when dried. Such noncoalescablepolymer particles include materials such as polystyrene particles andcan optionally be present in the water insoluble component of thecompositions at concentrations such that they do not interfere with thereinforcement effects of the coalescable water insoluble polymerparticles.

The water insoluble polymer particles comprise from about 3% to about75% by weight of the solids content of the compositions of the inventionwith 10% to 66% being preferred and 20% to 50% being most preferred.

While applicants do not wish to be limited by any theory, it is believedthat the coalescable water insoluble polymer particles reinforce andprovide beneficial properties to the films of the invention by absorbingstresses and strains during and after film formation. Additionally, bymaintaining the water insoluble particles in a noncoalesced statethroughout drying, shrinkage of the film, which would normally occur, issubstantially reduced. Further, the formation of relatively largedomains of coalesced water insoluble particles within the film isprevented, resulting in a more uniform structure and film surface. Thisuniformity results in more uniform wetting when the surface of the filmis wetted with a wide variety of materials. This provides an advantagewhen the reinforced film of this invention is applied as a coatingbinder for coating paper for offset lithography and other printingprocesses. Relatively large scale variability in the surface of thepaper leads to differences in wettability during printing by aqueousfountain solution and non-aqueous ink. Conventional binders comprisinglatex and starch in which the latex particles coalesce during dryinglead to variations in surface wettability. This phenomenon is known inthe paper coating art as binder migration, and can result in theprinting defect known as mottle.

In practice of the invention, it is preferred that the majority of waterinsoluble polymer particles have a particle size less than 1 micron withit being particularly preferred that at least 90% of the particles havea particle size of less than 0.5 microns and most preferred that atleast 90% of the particles have a particle size of less than 0.3microns. Although smaller water insoluble polymer particles have agreater tendency to coalesce, they also provide superior reinforcingproperties in comparison to an equal mass of larger particles.

The invention is seen as being able to broadly use a variety of waterinsoluble particles. In particular, particles formed from diene andother unsaturated (vinyl) monomers are suitable for use according to theinvention. Such diene monomers include 1,3-butadiene, isoprene,chloroprene, cyclobutadiene and divinyl benzene. Suitable unsaturatedmonomers include alkyl acrylates, hydroxylated alkyl methacrylates,alkyl vinyl ketones, substituted acrylamides, methacrylic acid,N-methylol acrylamide, 2-hydroxyethyl acrylate, crotonic acid, itaconicacid, fumaric acid, maleic acid, maleic anhydride, vinyl halides,vinylidene halides, vinyl esters, vinyl ethers, vinyl carbazole, N-vinylpyrrolidone, vinyl pyridene, chlorostyrene, alkyl styrene, ethylene,propylene, isobutylene, vinyl triethoxy silane, vinyl diethylmethylsilane, vinyl methyl dichloro silane, triphenyl vinyl silane,1-vinyl-1-methysilia-14-crown-5. Preferred monomers include methylmethacrylate, vinyl acetate, acrylonitrile, acrylic acid, acrylamide,maleic anhydride, monovinyl silicon compounds including vinyl trimethylsilane, ethyl vinyl ether, chlorostyrene vinyl pyridine, butyl vinylether, 2-ethylhexyl acrylate, isoprene, chloroprene, with vinylidenechloride, butyl vinyl ether and styrene being particularly preferred,and styrene being most preferred.

Of the polymer particles prepared by polymerizing monomers in the abovegroup, particularly preferred are those prepared from ethylene and vinylacetate and 1,3-butadiene and styrene. Styrene-butadiene latices areparticularly preferred and include pure styrene-butadiene latices aswell as copolymers of styrene and butadiene with other monomers.

These water insoluble polymer particles can be prepared independentlyand later mixed in wet or dry state with a water soluble component orthey can be prepared by carrying out a reaction in the presence of thewater soluble polymers such as disclosed in U.S. Patent No. 5,003,022,the disclosure of which is hereby incorporated by reference. This patentdiscloses graft copolymers which are the reaction products of thinnedgelatinized starch and one or more vinyl grafting monomers, said vinylgrafting monomers comprising at least 10% diene by weight. It isbelieved that the polymerization reactions carried out in the presenceof starch and other water soluble polymers according to the inventioncan result in grafting of unsaturated monomers to molecules of the watersoluble polymers such as starch. Accordingly, "reaction product" as usedherein should be considered as encompassing starch graft copolymers whenreferring to the products of the peroxide and persulfate initiatedreactions described herein.

Chain Transfer Agents

Where the dispersion comprises a "reaction product," conventional chaintransfer agents, known to the synthetic rubber industry as "modifiers,"may be employed to regulate the molecular weight of the polymer formed.Suitable chain transfer agents include materials such as n-dodecylmercaptan, n-cetyl mercaptan, bromoform, carbon tetrachloride and thelike in amounts ranging from 0.01 to about 5 percent of the monomerweight, with 0.10 to about 1% being preferred.

Initiators

Initiators (catalysts) suitable with the present invention include thosematerials which act to initiate free radical polymerization on and inthe presence of starches and other water soluble polymers to yield theaqueous dispersions of the present invention. The initiation ofpolymerization on the water soluble polymers can result in grafting.Suitable initiators include organic and inorganic peroxy compounds, azocompounds and persulfate compounds. Hydrogen peroxide and persulfate ionfree radical initiators are preferred, with potassium persulfate beingparticularly preferred to use with derivatized and/or thinned starchesaccording to the methods of the present invention. Persulfates may beused in amounts of at least about 0.01% of the weight of monomers used,but are preferably used in a range of from about 1% to about 10%.Persulfates may be used in solid form. Such use allows production ofdispersions with higher solids contents. The persulfate initiator may beused alone or in a mixture with other initiators. In addition, theinitiator can be added at once or over the course of the polymerizationtime.

It is sometimes the case that reducing agents are required to activatethe decomposition of the above-identified free-radical initiators.Suitable reducing agents may include ferrous ammonium sulfate, ascorbicacid, sodium bisulfite, sodium metabisulfite and sodium thiosulfate.These reducing agents can be added at once at the beginning or duringthe course of the reaction.

Surfactants

Surfactants may be used to stabilize the aqueous dispersion and can beadded either before reaction or after the reaction is complete. Suitabletypes of surfactants include anionic, cationic, amphoteric and nonionicsurfactants. Care should be used in selecting the surfactant such thatit not interfere with the reaction or with the use of the finaldispersion in the process of paper coating such as by flocculation ofthe clay or providing undesirable viscosity in the dispersion.Surfactants may generally be used at levels up to about 10% of themonomer weight, with a level of about 0 to 5% being preferred for use ofsodium dodecyl benzene sulfonate.

Reaction Conditions

In the case where the polymeric dispersions of the invention are theproducts of a free radical initiated polymerization reaction carried outin the presence of a water soluble polymer, that polymer is preferably athinned derivatized starch. The starches used according to this aspectof the invention are gelatinized by cooking at a solids content ofbetween 20 and 40% (dry basis), with a solids content of between 30 and40% being especially preferred. The cooked, gelatinized, thinned starchpaste is then placed in a reaction vessel capable of containing andwithstanding the pressure of the reaction. Regardless of whether starchor other water soluble polymers are used, a variety of monomers can bereacted to form the polymeric dispersions of the invention. A preferredcombination of monomers is styrene and 1,3-butadiene. Because of therelatively high volatility of 1,3-butadiene, it (and other gaseousmonomers) is reacted under pressure. In general, the more 1,3-butadienepresent in the reaction mixture, the higher the pressure at which thereaction is run. Maximum pressures during the reaction are generallybetween 25 and 300 psig (or more).

One or more surfactants may be added at any time during the reactionprocess. Preferred amounts, when added, range to as high as 10% based onthe total monomer weight, with amounts ranging from 1 to 5% beingespecially preferred.

The free radical initiator or initiators can be added at any time duringthe reaction process. A preferred method of free radical initiatoraddition would have from 1 to 5% (based on total monomer weight) addedto the water soluble polymer prior to monomer addition, with up to 5%(based on total monomer weight) being added in increments during thereaction.

The total unsaturated monomer to water soluble polymer weight ratio inthe aqueous dispersion is preferably between about 2:10 and about 30:10,and a ratio of between about 6:10 and 8:10 being most preferred.1,3-Butadiene can be reacted with water soluble polymers in the presenceof other monomers. When 1,3-butadiene and styrene are used as theunsaturated monomers, the amount of 1,3-butadiene preferably ranges fromat least 10% and preferably up to about 70% by weight of the monomers.Most preferably, the 1,3-butadiene is present at weight concentrationsof from about 20% to about 40% in combination with styrene inconcentrations of from about 60% to about 80%. The monomer or monomerscan be added at the beginning or during the course of polymerization,depending on reaction conditions. The monomers are preferably addedafter the addition of the surfactant and the free radical initiator.Preferably, the less volatile reactants are added first and the morevolatile reactions are added last.

The water soluble polymer/unsaturated monomer reaction can be carriedout over a wide temperature range depending on the type of monomers andinitiators used. Normally the temperatures would range from 25° to 120°C., with a reaction temperature range of 50° to 90° C. being preferred.The reaction mixture is preferably stirred while it undergoes heating.

A reaction time ranging from about 0.5 to 24 hours after addition of theinitiator is usually adequate to produce a final dispersion withsuitable properties. In particular, a reaction time of from about 2 toabout 12 hours has been found to be particularly preferred for theproduction of suitable product.

It is desired that the level of residual monomers is minimized in thefinal reacted product. Accordingly, a post reaction treatment may benecessary. A preferred treatment comprises the incorporation ofadditional initiator. The use of steam-vacuum distillation has beenfound to lower residual styrene concentrations while providing a productwith lower viscosity and higher solids. Another method comprisescarrying out the reaction at 70° C. for three hours and then at 90° C.for two hours with steam vacuum distillation, while still another methodcomprises use of a jet cooker to efficiently remove residual monomer.

Coating Colors

Products of the invention in the form of redispersible dry powders canbe used advantageously as binders in paper coating processes. Coatingcolor compositions typically comprise pigments such as clay along withbinders and a variety of specialty additives such as crosslinkers andlubricants. The liquid coating color is then applied to paper substratesusing methods well known in the art and illustrated in several of theexamples below.

The binder portion of the coating color typically comprises a blend oflatex and starch with latex typically being used as an emulsion atapproximately 50% solids. While it is generally desired to use binderswith higher solids contents, such binders are not widely available.Starch used in coatings is generally gelatinized or cooked in water atabout 30% solids or less. Pigments can be supplied dry or asapproximately 70% solids slurries. Thus, when formulating coatingcolors, total solids can be limited by the amount of water introduced byeach of the color components, and it may be very difficult or expensiveto raise solids to the maximum which can be run on the particularcoating equipment.

The dry redispersible powder of the present invention makes it possibleto eliminate the water which normally accompanies the latex and starchpresent in a coating color, and thereby greatly simplifies preparingcoating colors having very high solids levels. Not only does less waterneed to be removed during the drying operation, but the reduced watercontent leads to a reduction in gross shrinkage of the coating on thepaper on drying. The improved reduced water content improves smoothnessand uniformity of the paper coating. The dry redispersible powder of theinvention can be redispersed in water at a solids level substantiallyhigher than the original dispersion, and used as such to formulate highsolids coating having 60% solids levels or higher. Alternatively, thepowder can be added, with mixing, directly to an aqueous slurry ofpigment to redisperse the powder in the presence of the pigment. Evenwhen high solids colors are not desired, the powder can be used toadvantage in formulating coating colors in any range of solids, and thecoating color so created is virtually indistinguishable from a coatingcolor made using the original dispersion prior to drying.

If the dry powder of this invention is used in its most preferred form,the coating color so created is virtually indistinguishable from acoating color made using the original dispersion prior to drying, asdeterminedby examining the properties of paper coated in a similarmanner with both colors.

For the purpose of this invention, film refers to a film having a smoothsubstantially planar continuous surface. While the film can comprisesome substantial cracking, it is recognizable to the naked eye as aplanar film and not as a powder or particulate coating. A water solublepolymer film is a film wherein the continuous phase consists essentiallyof water soluble polymer.

For the purpose of this invention, a water insoluble polymer particle isconsidered "coalescable" if a film cast from such polymer particlesdispersed in water requires a temperature no higher than 85° C. tocoalesce at atmospheric pressure. Particles are considered to coalesceif there is a substantially irreversible combination of particlesinvolving deformation and merging of polymer chains across the particleboundaries to create long range order. Where an aqueous dispersioncomprises a blend of water soluble and water insoluble components, thecoalescability of the water insoluble polymer particles may bedetermined by testing a film of the water insoluble component in theabsence of the water soluble components which might comprise componentswhich inhibit coalescence.

Where the aqueous dispersion comprises a reaction product, such as agraft copolymer, of water soluble and water insoluble components, it maynot be possible to separate all those water soluble components thatinhibit coalescence from the water insoluble polymer particles.Accordingly, the coalescability of the reaction product water insolublepolymer particles is determined by evaluation of the coalescability ofthe polymer particles that would have resulted from carrying out thepolymerization reaction in the absence of the water soluble components.

For example, where the water insoluble polymer particles are produced bya styrene/butadiene starch graft polymerization reaction, the particlesare considered coalescable if the reaction product of an equivalentstyrene/butadiene polymerization reaction would have been coalescable.

For the purpose of this invention, a material is considered completelyredispersible if it has essentially the same physical properties afterit has been dried and redispersed without heating or extreme agitationas it exhibited as an aqueous dispersion before it was dried. A materialis considered completely redispersible if it passes the following test.According to this test, a dried film or powder is placed on a microscopeslide where it is examined under a binocular microscope with amagnification range of 10-70×. A drop of distilled water at roomtemperature is placed on the slide and the film or powder is observedover a 10 minute period. The ability of the dried material to disperseinto the drop of water is then evaluated. Where the material contactedby the drop appears to form a white dispersion of particles similar inappearance to a latex without the application of heat, agitation, orprobing, the material is considered to be completely redispersibleaccording to the invention. Furthermore, the material is considered tobe both completely and readily redispersible if it appears to turn towhite "smoke" when contacted by water and the components, both watersoluble and insoluble, travel into the water drop rapidly at thebeginning of the 10 minute test without application of heat, agitationor probing. Thus, readily redispersible materials are a special subsetof completely redispersible materials where the redispersion phenomenonoccurs especially rapidly. In order to pass these tests, it is notnecessary that all the film or powder contacted by the drop of water bedispersed by the single drop of water. Nevertheless, if the film merelywhitens or breaks into chunks or requires probing to break up and doesnot produce "smoke" or a white dispersion of particles as describedabove, it does not qualify as being completely or readily dispersible.

Based on the above definitions of redispersibility, it is discoveredthat a number of starch/unsaturated monomer reaction products, includinga commercial starch grafted copolymer, PENGLOSS® (Penford Products Co.,Cedar Rapids, Iowa), and blends of commercial latex polymer particlesand carbohydrates, exhibit the unusual ability to be dried to produce afilm or powder and be completely and readily redispersed. The ability ofa film to redisperse is dependent on the type of water soluble polymerused, the size of the polymer molecule, the nature and amount ofsubstitution on the polymer, the type of water insoluble polymerparticle with which it is combined, or the type and amount(s) ofmonomer(s) with which it is reacted, and the method used to dry thematerial. According to one aspect of the invention, certain substitutedand/or thinned water soluble polymers exhibit the ability to stabilize alatex dispersion. In addition, it has been found that the water solublepolymers allow the starch/vinyl monomer reaction product or blends ofcommercial latices and substituted and/or thinned carbohydrates to bedried and redispersed such that the materials have essentially the samephysical properties, including particle size, after they have been driedand redispersed as they had before they were dried to form a film orpowder.

Completely redispersible films and powders according to the inventioninclude latex/carbohydrate blends or starch/unsaturated monomer reactionproducts, that are used as binders in coating color compositions inpaper coatings. Papers coated with coating colors containing bindersmade from redispersed materials would have essentially the sameproperties, as measured by gloss and dry pick strength, as the paperscoated with coating colors containing binders made from the samematerials before they were dried and redispersed.

EXAMPLES

Example 1 discloses water soluble films reinforced with increasingamounts of coalescable water insoluble particles. Example 2 disclosestransmission electron micrographs of dispersions of the invention beforeand after drying and redispersion. Example 3 discloses scanning electronmicrographs of films with and without substantially noncoalesced polymerparticles.

Example 1

In this example, blends of a coalescable styrene/butadiene latex with aT_(g) of 12.0° C. (Dow 620 latex, Dow Chemical Co., Midland, Mich.) andan enzyme thinned lightly oxidized hydroxyethyl starch ether producthaving a DE of 10 (enzyme thinned Pencote®, Penford Products Co., CedarRapids, Iowa) were blended at various ratios and dried to producereinforced films. The styrene/butadiene latices in these films werenoncoalesced and served to reinforce the films and relieve crackingstresses.

Referring to FIG. 1a, a film comprising 100% of the thinned starch andno latex is significantly cracked and crazed. Referring to FIG. 1b, thefilm comprising 3% latex particles is considered to constitute a watersoluble polymer film reinforced with coalescable polymer particlesaccording to the invention. The presence of even 3% elastomeric latexparticles is seen to produce a better film by absorbing and relievingshrinkage stresses. Even though the film includes numerous cracks, thenature of the film is such that it provides improved properties to papercoating colors in which it is incorporated as a binder.

FIG. 1c discloses a film comprising 6% latex which has a smoothersurface and fewer cracks. FIGS. 1d, 1e, 1f, 1g and 1h disclose,respectively, films comprising 12%, 24%, 30%, 40% and 60% latex,illustrate further improved film properties and reinforcement and stressrelief provided by the noncoalesced latex particles. By the time thelatex concentration reached 30% by weight, the film is almost totallysmooth and devoid of cracks. At 40% and 60% concentrations, the filmsare devoid of all cracks.

Example 2

In this example, electron microscopy was used to examine the particlesof a dispersion comprising styrene-butadiene/starch reaction product anda physical blend of Dow 620 latex with enzyme thinned starch, before andafter drying and redispersion.

Films of a styrene-butadiene/starch reaction product dispersion with amonomer/starch ratio of 60/100, a solids of 45.6% dry substance basisand a T_(g) of 14.5° C. (PENGLOSS® binder, Penford Products Co., CedarRapids, Iowa), and a physical blend of Dow 620 latex and enzyme thinnedlightly oxidized hydroxyethyl starch ether product (enzyme thinnedPencote®), at a latex/starch ratio of 62/100 and a solids of 45% drysubstance basis, were dried at room temperature and redispersed with ionexchanged water. For the electron microscopy examination, thedispersions were diluted to 0.5% solids with distilled water, and asmall drop of each sample was sandwiched between two copper sheets,fast-frozen in a liquid cryogen and transferred to a vacuum chamberequipped with a cold stage. There, the sample was fractured, etched andthen coated with an ultra-thin, conducting platinum and carbonsupporting film. The metal film was then removed, cleaned with acid andwashed thoroughly with distilled water. The metal supporting film whichcontains the shadows of dispersion particles was then imaged in aTransmission Electron Microscope (TEM), (model H-7000, Hitachi). FIG. 2ashows a TEM photograph of styrene-butadiene/starch reaction productdispersions of PENGLOSS® binder at 20,000× and FIG. 2b showsreconstituted PENGLOSS® binder at 20,000×. FIG. 3a illustrates the TEMof Dow latex-enzyme thinned starch blend and FIG. 3b shows itsreconstituted product at 10,000×. It is clearly indicated that afterbeing dried and redispersed, the polymer particles of these dispersionsare noncoalesced and still maintain their original distinct sizes andshapes.

Example 3

In this example, various films were evaluated by means of a scanningelectron microscope to directly determine whether water insolublepolymer particles were coalesced. While films that are readily orcompletely dispersible will necessarily have noncoalesced polymerparticles, there can still exist films having noncoalesced particleswhich are not readily dispersible. Such films include those thatcomprise retrograded starch or a crosslinked water soluble component.

Films were produced from dispersions including (A) a 100%styrene/butadiene latex dispersion (Dow 620 Latex); (B)styrene/butadiene latex (Dow 620 Latex) blended at a 1:2 weight ratiowith a thin hydroxyethyl starch ether product (Pencote® starch); (C)styrene/butadiene latex (Dow Latex 620) blended at a 1:2 weight ratiowith an enzyme thinned hydroxyethyl starch ether product (E.T. Pencote®starch) which was significantly thinner than the product of (B); and astyrene/butadiene starch graft copolymer dispersion (PENGLOSS® binder)comprising 1 part initial monomer per 2 parts starch.

The dried films were fractured so the freshly fractured edge could beexamined. In cases where the wafer was too pliable to fracture easily,the samples were dipped momentarily into liquid nitrogen and thenfractured. The fractured slivers and a flat wafer piece were mounted onstubs using copper tape. The slivers were oriented so that the fracturedsurface faced up to allow easy examination. The specimens weresputter-coated for 3 minutes with gold-paladium in the presence of Argongas prior to examination in the JEOL JSM-840 scanning electronmicroscope.

Referring to FIGS. 4a-4d, the latex particles of the 100% latex film inFIG. 4a are seen to be entirely coalesced in contrast to the polymerparticles of the films produced by the latex/enzyme thinned starch blendof FIG. 4c and the starch graft copolymer of FIG. 4d. The latexparticles of the latex/starch blend of FIG. 4b are substantiallycoalesced. The coalesced particles render the film not completelydispersible. As such, that film is not considered to fall within thescope of the invention.

In Examples 4-9, various blends of water soluble and water insolublecomponents were prepared as aqueous dispersions. Films were cast fromthe resulting dispersions and examined as described below to determinethe degree of redispersibility of the dried film. Based on thoseexaminations, conclusions were drawn regarding coalescence of thecoalescable water insoluble polymer particles present in those films.Specifically, where the dried film remained intact and failed to bereadily and/or completely redispersible, it was concluded that the waterinsoluble polymer particles in the film had coalesced. Such conclusionscan be drawn because a film in which the water insoluble polymerparticles are coalesced is neither readily nor completely redispersible.In cases where the dried film partially dispersed upon application of adrop of water and the film remained mainly intact, it was concluded thatthe insoluble polymer particles had partly or mainly coalesced. Where afilm was readily or completely dispersible upon application of a drop ofdistilled water, it was concluded that the insoluble polymer particleshad not coalesced.

Example 4

Blends were created from among the following materials: a commercialavailable carboxylated styrene-butadiene latex (Dow CP620NA), a solutionof cooked Pencote® starch, and a dextrose solution. Blends were made inthe ratios (solids basis) by weight described in Table 1 below. A latexonly sample was included as a control (A).

                  TABLE 1                                                         ______________________________________                                                   (Parts by Weight)                                                             A       B     C        D   E                                       ______________________________________                                        Dow 620 Latex                                                                              100       30    30     30  80                                    Pencote ® Starch                                                                       --        70    67     64  --                                    Dextrose     --        --     3      6  20                                    ______________________________________                                    

Films of the materials described above were cast on glass microscopeslides and allowed to dry thoroughly at room temperature (about 70° F.)for 18 hours. The dispersions of Runs A-D dried to dried tosubstantially uniform crack-free films. Dispersion E was very slow todry as a result of the water forming properties of the dextrose, and didnot form a film. The dried samples were then examined under a binocularmicroscope with a magnification range of 10-70× in the followingfashion. A drop of distilled water at room temperature was placed on thesample and observed over a 10 minute period. The following observationswere made as to the redispersibility of the wetted samples, andconclusions were drawn as to the coalescence of water insolubleparticles in the samples.

                  TABLE 2                                                         ______________________________________                                        Film    Microscopic Observation                                                                            Conclusion                                       ______________________________________                                        A       Film remains intact. Coalesced                                        B       Film remains intact. Coalesced                                        C       Film is less tough than B but                                                                      Mainly                                                   remains intact.      Coalesced                                        D       Film readily disperses. A milky                                                                    Not                                                      dispersion of particles is                                                                         Coalesced                                                apparent within a few seconds.                                                Nearly complete to complete                                                   redispersibility.                                                     E       Sample readily disperses. A                                                                        Not                                                      milky dispersion of latex is                                                                       Coalesced                                                immediately apparent. Complete                                                redispersibility.                                                     ______________________________________                                    

Example 5

Blends were created from among the following materials: a commerciallyavailable carboxylated styrene-butadiene latex (Dow CP620NA availablefrom Dow Chemical Co.), a solution of a cooked Pencote® starch, a thin,lightly oxidized hydroxyethyl starch ether product (supplied by PenfordProducts Co.) and a solution of enzyme-thinned Pencote® (ET Pencote®)starch, Penford Products Co. Blends were made in the ratios (solidsbasis) described in Table 3 below.

                  TABLE 3                                                         ______________________________________                                                   (Parts by Wt.)                                                                A      B     C        D   E                                        ______________________________________                                        Dow 620 Latex                                                                              30       30    30     30  --                                     Pencote ® Starch                                                                       70       67    61      0  --                                     ET Pencote ®                                                                            0        3     9     70  --                                     PENGLOSS ®                                                                             --       --    --     --  100                                    ______________________________________                                    

The dispersions described above were cast on glass microscope slides andallowed to dry thoroughly at room temperature. A film of PENGLOSS®binder (Penford Products Co., a styrene/butadiene enzyme thinned starchreaction product produced according to the methods of U.S. Pat. No.5,003,022) designated as "E" was included in the comparison. The driedfilms were continuous and crack free. Films were then examined under abinocular microscope with a magnification range of 10-70× in thefollowing fashion. A drop of distilled water was placed on each filmwhich was observed over a 10 minute period to determine if it wasreadily dispersible. The following observations were made.

                  TABLE 4                                                         ______________________________________                                        Film    Observation        Conclusion                                         ______________________________________                                        A       Film remains intact and                                                                          Coalesced                                                  tough.                                                                B       Film though less tough                                                                           Coalesced                                                  than A, remains mainly                                                        intact.                                                               C       Film disperses. A milky                                                                          Not Coalesced                                              dispersion of particles is                                                    apparent within a few                                                         minutes. Nearly complete                                                      to complete                                                                   redispersibility.                                                     D       Film is readily    Not Coalesced                                              dispersible and a milky                                                       dispersion of particles                                                       is immediately apparent.                                                      Complete redispersibility.                                            E       Film is readily    Not Coalesced                                              dispersible and a milky                                                       dispersion of particles                                                       is immediately apparent.                                                      Complete redispersibility.                                            ______________________________________                                    

Example 6

Blends were created from among the following materials: a commerciallyavailable carboxylated styrene-butadiene latex (Dow CP620NA availablefrom Dow Chemical Co.), a solution of partially hydrolyzed polyvinylalcohol (Airvol 203-Air Products & Chemicals Inc.) and a dextrosesolution. Blends were prepared in the ratios (solids basis) described inTable 5 below.

                  TABLE 5                                                         ______________________________________                                                      (Parts by Weight)                                                             A   B          C     D                                          ______________________________________                                        Dow 620 Latex   30    30         30  70                                       Polyvinyl Alcohol                                                                             61    64         70  30                                       Dextrose         9     6         --  --                                       ______________________________________                                    

Dispersions of the materials described above were cast on glassmicroscope slides and allowed to dry thoroughly at room temperature. Thedried films were smooth and continuous. Films were then examined under abinocular microscope with a magnification range of 10-70× in thefollowing fashion. A drop of distilled water was placed on the film andthe film was observed over a 10 minute period. The followingobservations were made.

                  TABLE 6                                                         ______________________________________                                        Film   Observation          Conclusion                                        ______________________________________                                        A      Film readily disperses. A                                                                          Not Coalesced                                            milky dispersion of particles                                                 is immediately formed.                                                 B      Film readily disperses. A                                                                          Not Coalesced                                            milky dispersion of particles                                                 is immediately formed.                                                 C      Film readily disperses. A                                                                          Not Coalesced                                            milky dispersion of particles                                                 is immediately formed.                                                 D      Film shortly becomes non-                                                                          Not Coalesced                                            coherent and a milky dispersion                                               of particles soon develops.                                                   The film was completely                                                       redispersible.                                                         ______________________________________                                    

Example 7

Blends were created from among the following materials: a commerciallyavailable carboxylated styrene-butadiene latex (Dow CP620NA availablefrom Dow Chemical Co.), a solution prepared from guar gum (Jaguar gumHP-8 Rhone Poulenc Inc.), a solution of hydroxypropyl methylcellulose(methocel J12MS--Dow Chemical Co.), a dextrose solution and a solutionof enzyme-thinned Pencote® starch (ET Pencote®). Blends were made in theratios (solids basis) described in Table 7 below.

                  TABLE 7                                                         ______________________________________                                                   (Parts by Weight)                                                             A   B        C     D     E   F                                     ______________________________________                                        Dow Latex 620                                                                              30    30       30  30    30  30                                  Guar Gum     --    --       --  70    64  61                                  Methocel     70    64       61  --    --  --                                  Dextrose     --    6        --  --    6   --                                  ET Pencote ®                                                                           --    --       9   --    --   9                                  ______________________________________                                    

Dispersions of the materials described above were cast on glassmicroscope slides and allowed to dry thoroughly at room temperature toform films. Films were then examined under a binocular microscope with amagnification range of 10-70× in the following fashion. A drop ofdistilled water was placed on each film and the film was observed over a10 minute period. The following observations were made.

                  TABLE 8                                                         ______________________________________                                        Films    Observation         Conclusion                                       ______________________________________                                        A        Film breaks up but doesn't                                                                        Coalesced                                                 redisperse; remains generally                                                 intact.                                                              B        Filmdisperses as methocel                                                                         Noncoalesced                                              dissolves. Milky dispersion of                                                particles is soon apparent.                                                   The film was completely                                                       redispersible.                                                       C        Filmdisperses as methocel                                                                         Noncoalesced                                              dissolves. Milky dispersion of                                                particles is soon apparent.                                                   The film was completely                                                       redispersible.                                                       D        Film breaks up but doesn't                                                                        Coalesced                                                 redisperse; remains generally                                                 intact.                                                              E        Film disperses as quar gum                                                                        Noncoalesced                                              dissolves. Milky dispersion of                                                particles soon becomes                                                        apparent. The film was                                                        completely redispersible.                                            F        Film disperses as guar gum                                                                        Noncoalesced                                              dissolves. Milky dispersion of                                                particles soon becomes                                                        apparent. The film was                                                        completely redispersible.                                            ______________________________________                                    

Example 8

Blends were created from among the following materials: a commerciallyavailable carboxylated styrene-butadiene latex (DOW CP620NA) availablefrom Dow Chemical Co.), a solution of Polyethylene glycol 1000(PEG-1000) and a solution of maltodextrin with a dextrose equivalent of10 (Maltrin 100--Grain Processing Co.). Blends were made in the ratios(solids basis) described in Table 9 below. A latex only sample wasincluded as a control (C).

                  TABLE 9                                                         ______________________________________                                                   (Parts by Weight)                                                             A          B     C                                                 ______________________________________                                        Dow 620 Latex                                                                              30           30    100                                           PEG 1000     70           --    --                                            Maltrin 100  --           70    --                                            ______________________________________                                    

Dispersions of the materials described above were cast on glassmicroscope slides and allowed to dry thoroughly at room temperature. Thedried films were smooth and continuous. Films were then examined under abinocular microscope with a magnification range of 10-70× in thefollowing fashion. A drop of distilled water was placed on the film andthe film was observed over a 10 minute period. The followingobservations were made.

                  TABLE 10                                                        ______________________________________                                        Film    Observation       Conclusion                                          ______________________________________                                        A       Film partially disperses. A                                                                     Partly Coalesced                                            milky dispersion of some                                                      particles forms.                                                      B       Film readily disperses; a                                                                       Not Coalesced                                               milky dispersion of                                                           particles is immediately                                                      formed.                                                               C       Film remains intact.                                                                            Coalesced                                           ______________________________________                                    

Example 9

Blends were created from among the following materials: a commerciallyavailable carboxylated styrene-butadiene latex (Dow CP620NA availablefrom Dow Chemical Co.), a vinyl acetate-ethylene copolymer latexemulsion with a T_(g) of about 5° C. (Airflex 500--Air Product &Chemicals Inc.) a natural rubber latex with a T_(g) that is unreportedbut is substantially below -20° C. (H-1400--Heveatex Corp.), a neoprenelatex with a T_(g) that is unreported by is substantially below -20° C.(Neoprene Latex 654, DuPont) and enzyme-thinned Pencote® starch. Blendswere made in the ratios (solids basis) as described in Table 11 below.Samples of all four latexes were included as controls (D, E, F & G).

                  TABLE 11                                                        ______________________________________                                                 (Parts by Weight)                                                             A    B     C      D    E    F     G                                  ______________________________________                                        Dow 620 Latex                                                                            --     --    --   100  --   --    --                               Airflex 500                                                                              50     --    --   --   100  --    --                               Natural Rubber                                                                           --     50    --   --   --   100   --                               Latex (Heveatex                                                               H-1400)                                                                       Neoprene Latex                                                                           --     --    30   --   --   --    100                              (DuPont 654)                                                                  E. T. Pencote ®                                                                      50     50    70   --   --   --    --                               ______________________________________                                    

Dispersions of the materials described above were cast on glassmicroscope slides and allowed to dry thoroughly at room temperature toform films. The were then examined under a binocular microscope with amagnification range of 10-70× in the following fashion. A drop ofdistilled water was placed on the film and the film was observed over a10 minute period. The following observations were made illustrate thatlatices vary in their tendency to coalesce and that large proportions ofwater soluble polymers will not necessarily inhibit coalescence oflatices with very low T_(g) s. T_(g) is a primary factor that affectsthe coalescability of water insoluble polymer particles. Other factorsinclude molecular weight, degree of crosslinking, particle size andsurface character.

                  TABLE 12                                                        ______________________________________                                        Film   Observation        Conclusion                                          ______________________________________                                        A      Film remains intact for                                                                          Partly Coalesced                                           some time but after several                                                   minutes, it becomes less                                                      intact and releases a milky                                                   dispersion of particles.                                               B      Film remains mostly intact                                                                       Largely Coalesced                                          and rather tough.                                                      C      Film remains intact for                                                                          Partly Coalesced                                           some time but after several                                                   minutes, it becomes less                                                      intact and releases a milky                                                   dispersion of particles.                                               D      Film remains intact.                                                                             Coalesced                                           E      Film remains intact.                                                                             Coalesced                                           F      Film remains intact.                                                                             Coalesced                                           G      Film remains intact.                                                                             Coalesced                                           ______________________________________                                    

In Examples 10-16, various monomers were reacted in the presence of athinned starch to produce aqueous polymeric dispersions. These reactionproducts including starch graft copolymers were then dried to producefilms and tested for dispersibility.

Example 10

In this example, a thin, lightly oxidized hydroxyethyl starch etherPencote® (Penford Products Co., Cedar Rapids, Iowa), was enzyme thinnedand reacted with butadiene and methylmethacrylate (10A) or withbutadiene and acrylonitrile (10B) in two 2 liter Parr reactors (ParrInstruments) in the presence of a potassium persulfate initiator toproduce a stable aqueous polymeric dispersion which was dried andredispersed.

In making the samples, a starch slurry containing 1200 grams dryPencote® starch was cooked in a laboratory bench cooker for about 30minutes at about 34.4% solids. The cooked starch was then cooled to 88°C. and thinned by adding 360 microliters of alpha-amylase (Canalpha,Biocon, Sarasota, Fla.) to the cooked starch paste. The mixture washeld, with stirring, at 88° C. for 1 hour and 40 minutes. To thismaterial, 3 ml hypochlorite (16% available chlorine) was added todeactivate the enzyme. According to this procedure, about 1307 grams ofthe cooked, thinned paste was added to two 2 liter (Parr Instrument)followed by 13.5 grams potassium persulfate and 173 grams water. To thefirst 2 liter reactor (Example 10A), 292 grams methylmethacrylate and158 grams butadiene were also added. To the second 2 liter reactor(Example 10B), 223 grams acrylonitrile and 227 grams butadiene were alsoadded. The mixtures were stirred and heated to about 70° C. and held for10 hours. The mixtures were allowed to cool to room temperature and thepH was adjusted to about 5.5 with dry Na₂ CO₃. The reaction productswere filtered through a 63 micron (0.0024 inches) screen.

Films were drawn of both products and allowed to air dry overnight. Thematerials were redispersed according to the following method. About 10grams of dried material were weighed into a 100 ml beaker. Enough ionexchanged water passed through a 0.2 micron filter was added to eachsample to bring total dry solids to about 15%. Each sample was stirredwithout heating for about 30 minutes and was checked for undissolvedmaterial. If all the material (or nearly all the material, i.e., greaterthan 99%), had gone into dispersion, the sample was filtered through a63 micron (0.0024 inches) screen and an estimate was made of the amountof undispersed material.

If the sample had a substantial amount of undispersed material (greaterthan 1 or 2%), heat was applied to the stirring material to raise thetemperature to 55°-75° C., and held for 15-60 minutes, depending on howquickly the sample appeared to disperse. The sample was then filteredthrough a 63 micron (0.0024 inch) screen to determine if all thematerial had dispersed. According to the above method, the film of 10Adispersed upon heating to 60° C. and produced less than 1% grit. Thefilm of 10B dispersed with no heat and produced less than 1% grit.Accordingly, while the film 10A ultimately redispersed under theapplication of mechanical agitation and heat, it would not have beenconsidered readily or completely redispersible according to the testmethod of Example 4 although it is believed that the film of 10B wouldhave been. Accordingly, it is concluded that the coalescable polymerparticles of film 10A were coalesced while those of film 10 B werenoncoalesced.

Example 11

In this example, the enzyme thinned starch ether was reacted withstyrene, butadiene and 2-ethylhexyl acrylate in a 2 liter Parr reactorin the presence of a potassium persulfate initiator to produce areaction product which was a stable aqueous polymeric dispersion.

Specifically, 1277 grams dry Pencote® starch was cooked in a laboratorybench cooker for about 30 minutes at about 38.1% solids. The cookedstarch was then cooled to 88° C. and thinned with 280 microliters ofalpha-amylase for 1 hour and 10 minutes. To this material was added 3 mlof hypochlorite (16% available chlorine) to deactivate the enzyme. To a2 liter Parr reactor was added about 1394 grams of the thinned starchpaste, 13.8 grams potassium persulfate, 7.2 grams NaHCO₃, 34 gramswater, 223 grams styrene, 106 grams butadiene and 16 grams 2-ethylhexylacrylate. The mixture was stirred and heated to about 70° C. and held atthis temperature for 8 hours. The mixture was cooled to room temperatureand the pH was adjusted to 7.0. A film was drawn of the reaction productmaterial and allowed to air dry overnight. The dry film was redispersedaccording to the method of Example 10. The film dispersed withoutheating and produced less than 1% grit. The film would have beenconsidered completely dispersible according to the method of Example 4and, therefore, it is concluded that the coalescable polymer particlesof that film were noncoalesced.

Example 12

In this example, an enzyme converted unmodified cornstarch (ET Pearl)was reacted with styrene and butadiene monomers in the presence of apotassium persulfate free radical initiator to produce a stable aqueouspolymeric dispersion. The material was then dried to form a film andredispersed.

Specifically, the pH of an unmodified, untreated starch slurrycontaining 1100 grams starch at 42% solids was adjusted to about 6.5with a concentrated Ca(OH)₂ solution. The slurry was thinned by adding280 microliters of alpha-amylase. The slurry and water was added to asteam heated starch cooker to give a final calculated solids of about37.0%. The water was heated to about 195° F. (with agitation) and thestarch/enzyme slurry was added just fast enough so that good mixingcould be maintained (about a 22 minutes total addition time). Thetemperature of the slurry was then maintained at 88° C. for about 40additional minutes. To this material was added 5 ml hypochlorite (16%available chlorine) to deactivate the enzyme. Evaporation of waterduring the cooling and thinning of the starch gave a final measuredsolids of about 45.5%. About 1222 grams of the cooked, thinned paste,13.8 grams potassium persulfate, 364.5 grams water, 233 grams styreneand 111 grams butadiene were added to a 2 liter Parr reactor. Themixture was stirred and heated to about 69° C. and held for 8 hours. Themixture was allowed to cool to room temperature and the pH was adjustedto about 5.5 with Na₂ CO₃. The reaction product was filtered through a63 micron (0.0024 inches) screen.

A film was drawn redispersed according to the procedure used in Example10. The dried material required heating to 60° C. to redisperse in waterand had less than 1% grit. The material would not have been consideredcompletely redispersible according to the test method of Example 4. Itis, therefore, concluded that the coalescable polymer particles of thatfilm were coalesced.

Example 13

In this example, Polaris LV (Penford Products Co., Cedar Rapids, Iowa),a thin hydroxyethyl potato starch ether was reacted with styrene andbutadiene in the presence of a potassium persulfate initiator to producea stable aqueous polymeric dispersion which was cast into a film, driedand redispersed.

A 38.3% solids starch slurry, containing 1100 grams dry substancePolaris LV, was thinned by adding 300 microliters of alpha-amylase. Theslurry was heated, with stirring, in a steam heated laboratory cooker to88° C. and held for about 1 hour and 30 minutes. The enzyme was thendeactivated with about 3 ml of hypochlorite (16% available chlorine).According to this procedure, about 1470 grams of cooked, thinned pastewas added to a 2 liter Parr reactor Na₂ CO₃, 15.5 grams water, 236 gramsstyrene and 92 grams butadiene. The mixture was stirred and heated to69° C. and held at this temperature for 8 hours. The mixture was allowedto cool to room temperature and the pH was adjusted to about 7.0. Thereaction product was filtered through a 63 micron (0.0025 inches)screen.

A film was drawn and redispersed according to the procedure used inExample 10. The film dispersed well without heating and produced lessthan 1% grit. It is believed that the film would have been consideredcompletely dispersible according to the test method of Example 4, and,therefore, it is concluded that the coalescable polymer particles ofthat film were noncoalesced.

Example 14

In this example, Amaizo 839 (American Maize Products Co., Hammond,Ind.), a highly thinned, waxy corn starch, was reacted with styrene andbutadiene in the presence of potassium persulfate initiator to produce astable aqueous polymeric dispersion.

Specifically, 752 grams dry Amaizo 839 starch was cooked in a laboratorybench cooker for about 2 hours 15 minutes at about 36.9% dry substancesolids. After cooling, 470 grams of the cooked paste was placed in a 1liter Parr reactor along with 4.7 grams potassium persulfate, 2.9 gramsNaHCO₃, 366 grams water, 76 grams styrene and 33 grams butadiene. Themixture was heated, with stirring, to about 69° C. and held at thistemperature for 8 hours. The mixture was cooled and filtered through a63 micron (0.0024 inch) screen. A film was drawn of the reaction productand allowed to air dry overnight. The dry film was redispersed accordingto the procedure used in Example 10. The film dispersed on heating to60° C. and provided less than 1% grit. It is believed that the materialwould not have been considered to be completely dispersible according tothe test method of Example 4, and, therefore, it is concluded that thecoalescable polymer particles of the film are coalesced.

Example 15

In this example, Star-Dri 5 (A.E. Staley Manufacturing Co., Decatur,Ill.), a waxy corn starch 5 DE maltodextrin, was reacted with styreneand butadiene in the presence of potassium persulfate initiator toproduce a stable aqueous polymeric dispersion.

Specifically, 270 grams dry Star-Dri 5 was combined with 442 gramswater, 6.6 grams potassium persulfate, 112 grams styrene and 53 gramsbutadiene in a 1 liter Parr reactor. The mixture was heated, withstirring, to about 69° C. and held at this temperature for 8 hours. Themixture was cooled and filtered through a 63 micron (0.0024 inches)screen. A film was drawn of the material and allowed to air dryovernight. The dry film was redispersed according to the procedure usedin Example 10. The film dispersed very well without heating and providedless than 1% grit. It is believed that the film would have beenconsidered completely dispersible according to the test method ofExample 4 and, therefore, it is concluded that the coalescable polymerparticles of the film are not coalesced.

Example 16

In this example, Dow 620 latex (Dow Chemical Co., Midland, Mich.), wascombined with a number of different types of modified corn starch. Theresulting dispersions were dried as films, redispersed and used as thebinder to prepare coating color compositions which were then coated ontopaper. These coated papers were then compared to papers which had beencoated with coating compositions made from the same dispersions beforethey had been dried and redispersed.

For this example, five sets of paper were coated. One half of each setconsisted of papers coated with coating color compositions made with abinder consisting of a dried and redispersed Dow 620 latex incombination with a modified corn starch. The other half of each setconsisted of papers coated with coating color compositions made with thesame binders, but after they had been dried and redispersed.

Specifically, Dow 620 latex was combined with five different modifiedcorn starches at a ratio of 38.3% dry weight Dow 620 latex to 61.7% dryweight of the modified corn starch. The latex and starch were combinedby slowly adding the latex to the starch with very good agitation. Thefirst set of papers (13A and 13B in Table 13) were coated with a coatingcolor composition made with a paper coating binder composition of 38.3%dry weight basis Dow 620 latex and 61.7 dry weight basis enzyme thinned,unmodified corn starch (ET Pearl). The ET Pearl starch was made usingthe same method as that used to produce the ET Pearl corn starch used inExample 12. The next set of papers (13C and 13D in Table 13) were coatedwith a coating color made with a paper coating binder composition of38.3% dry weight basis Dow 620 latex and 61.7% dry weight basis PenfordGum 290 starch (Penford Products Co., Cedar Rapids, Iowa). The PenfordGum 290 starch was cooked, but not enzyme thinned, in laboratory benchcooker using the method described in Example 11.

The next set of papers (13E and 13F in Table 13) were coated with acoating color composition made with a paper coating binder compositionof 38.3% dry weight basis Dow 620 latex and 61.7% dry weight basis StarDri 5 maltodextrin. The Star Dri 5 maltodextrin was first slurried inwater at 49% solids dry weight basis. The Dow 620 latex was thencombined with this slurry.

The next set of papers (13G and 13H in Table 13) were coated with acoating color composition made with a paper coating binder compositionof 38.3% dry weight basis Dow 620 latex and 61.7% dry weight basisFro-Dex 22 (American Maize Products Co., Hammond, Ind.). The Fro-Dex 22was first slurried in water at 50% solids dry weight basis. The Dow 620latex was then combined with this slurry.

The final set of papers (13I and 13J in Table 13) were coated with acoating color composition made with a paper coating binder comprising acooked Penford Gum 290 starch as described in Example 8 in combinationwith a slurry of CANTAB® corn syrup solids. (97 DE 95% dextrose cornsyrup solids, Penford Products Co., Cedar Rapids, Iowa) and water at aratio of 70% dry weight basis Penford Gum 290 and 30% dry weight basisCANTAB® corn syrup solids. Dow 620 latex was then added slowly to thismixture under agitation at a ratio of 38.3% Dow 620 latex to 61.7% drybasis of the Penford Gum 290 starch/CANTAB® corn syrup solids blend(38.3% Dow 620 latex, 43.2% Penford Gum 290 Starch, 18.5% CANTAB® cornsyrup solids).

The paper coating color compositions of this example were prepared bymixing the binders as described above, with a 70% solids clay slip andthen adjusting the pH to 8.3-8.8. The clay slip was prepared by addingNuclay (Englehard) to tap water containing a 0.04% polyacrylate/NaOHdispersant (42% solids) on the clay (commercial solids basis). Afteradding the above binders to the clay slip and adjusting the pH withammonium hydroxide, the coating colors were thoroughly mixed. A typicalcoating formula included:

    ______________________________________                                        Composition              Parts                                                ______________________________________                                        No. 1 delaminated clay (Nuclay)                                                                        100                                                  Binder                   18                                                   Total Solids             159-66%                                              pH                       8.3-8.8                                              ______________________________________                                    

A 28 lb. per 3,300 square foot unsized, uncalendered, base stock wascoated with the coating colors on a bench size trailing blade coater.Coating colors were applied at room temperature and immediately dried inan infrared dryer (CCR Enterprises, St. Louis, Mo.). Adjustments incoating weights were made by varying the trailing blade pressure. Allcoated samples were conditioned at 50% relative humidity and 23° C.before testing.

The coated sheets were calendered on a B.F. Perkins & Sons supercalender(Chicopee, Mass.). Calendering conditions were: roll pressure of 1000lb/linear inch; a roll speed of 78 feet per minute and a rolltemperature of 150° F. Each sheet was calendered through 4 nips.

After coating and calendering of the paper stock, it was tested forgloss and IGT. Gloss determinations were made by averaging roughly tenmeasurements per sheet for three or four coated and calendered sheets ofeach type on a 75° Glossgard II Glossmeter (Pacific Scientific, SilverSpring, Md.). IGT analysis were run on a Reprotest IGT PrintabilityTester (Reprotest North America, Cherry Hill, N.J.).

The results of testing the coating color compositions indicatesignificant differences in properties between the fresh and redispersedblends of Dow 620 latex with either enzyme thinned Pearl starch orPenford gum 290 starch. The dramatic increase in coating color viscosityshows that the dried blends of these materials did not completelyredisperse so as to duplicate the properties of the fresh bindermixtures. Accordingly, it can be concluded that at least some of thecoalescable polymer particles in the blend had coalesced.

In contrast, the blends of Star Dri 5 maltodextrin and Fro-Dex 22 starchhydrolyzate products with Dow 620 latex appeared to completelyredisperse given the equivalence of coating color dispersions comprisingthe fresh and redispersed blends. It was thus concluded that thecoalescable latex particles in the dried dispersions remainedsubstantially noncoalesced.

The Dow 620 latex/CANTAB® corn syrup solids/Penford Gum 290 blendexhibited a significant increase in viscosity upon drying andredispersion, indicating that the coalescable polymer particles failedto remain substantially noncoalesced.

                                      TABLE 13                                    __________________________________________________________________________                            Viscosity                                                                          Viscosity.sup.6                                                          of the                                                                             Coating                                                                  Coating                                                                            Color Coating.sup.7                              Run                     Colors                                                                             Solids                                                                              Solids                                                                             Gloss                                                                              IGT.sup.5                        No.                                                                              Binder Composition   (cps)                                                                              (%)   %    %    (cm/sec)                         __________________________________________________________________________    13A                                                                              Dow 620/ET Pearl (fresh)                                                                            690.sup.1                                                                         64.7  64.7 68.0 35                               13B                                                                              Dow 620/ET Pearl (redispersed)                                                                     1925.sup.1                                                                         65.0  62.5 69.2 37                               13C                                                                              Dow 620/PG 290 (fresh)                                                                             5450.sup.2                                                                         61.0  61.0 62.8 37                               13D                                                                              Dow 620/PG 290 (redispersed)                                                                       9200.sup.3                                                                         61.0  59.0 66.1 34                               13E                                                                              Dow 620/Star Dri 5 (fresh)                                                                         1320.sup.1                                                                         64.0  64   67.5 35                               13F                                                                              Dow 620/Star Dri 5 (redispersed)                                                                   1225.sup.1                                                                         64.0  64   67.3 34                               13G                                                                              Dow 620/Fro-Dex 22 (fresh)                                                                          190.sup.4                                                                         66.0  66   69.2 35                               13H                                                                              Dow 620/Fro-Dex 22 (redispersed)                                                                    172.sup.4                                                                         66.0  66   69.4 35                               13I                                                                              Dow 620/CANTAB/PG 290 (fresh)                                                                      2890.sup.2                                                                         62.0  62   62.59                                                                              37                               13J                                                                              Dow 620/CANTAB/PG 290 (redispersed)                                                                4980.sup.2                                                                         62.0  61   62.51                                                                              37                               __________________________________________________________________________     .sup.1 Model RVF Brookfield Viscometer, Spindle #3, 20 rpm.                   .sup.2 Model RVF Brookfield Viscometer, Spindle #4, 20 rpm.                   .sup.3 Model RVF Brookfield Viscometer, Spindle #5, 20 rpm.                   .sup.4 Model RVF Brookfield Viscometer, Spindle #2, 20 rpm.                   % Solids for viscosity determinations.                                        .sup.7 % Solids for coating operation.                                   

Example 17

In this example, a sample of PENGLOSS® binder (Penford Products Co.,Cedar Rapids, Iowa) was freeze-dried, redispersed and used as a binderin a coating color to coat paper.

The PENGLOSS® sample was first diluted to 20% solids with ion exchangedwater and then freeze-dried in a (Lyph-Lock 6 freeze drier (LabconcoCorporation, Kansas City, Mo.). The freeze-dried product was redispersedwith ion exchanged water at 50% solids. The redispersed material wasthen used as the binder in a coating color to coat paper according tothe method used in Example 16. The results are shown in Table 14 below.

                  TABLE 14                                                        ______________________________________                                        Coating Data for Redispersed Freeze-Dried PENGLOSS ®                                                   IGT                                              Sample              Gloss %  (ft/min)                                         ______________________________________                                        PENGLOSS ®      69.9     96.1                                             Redispersed PENGLOSS ®                                                                        68.0     91.3                                             ______________________________________                                    

Example 18

In this example, pilot plant prepared styrene-butadiene/starch reactionproduct (PENGLOSS® binder) was spray dried in a laboratory spray dryer.Specifically, PENGLOSS® binder was prepared from enzyme thinned Pencote®starch by reacting it with dry solids styrene and butadiene in theweight ratio of 100 parts E.T. Pencote® starch and 42 parts styrene/20parts butadiene. The reaction was initiated by 1.8% potassium persulfateon dry substance starch. The reaction mass was heated to 162° F. andheld at 160° F. for a total of 8 hours. The resulting PENGLOSS® binderhad a solids content of 50.4%.

The PENGLOSS® binder was spray dried in a laboratory Niro (NicholsEngineering Research Corp.) pilot spray dryer unit. The inlet air washeated by direct gas firing. The inlet temperature was set at 356° F.,and flow of PENGLOSS® binder started at a rate of 5 gal/hr. The exhausttemperature was 221° F. After the system equilibrated, samples werecollected. The material was screened through a standard 45 mesh screenbefore testing for redispersibility and coating data. Coating data wereobtained according to the procedure used in Examples 16 and 19. Coatingresults are shown in Table 15. These results show that the spray driedand redispersed PENGLOSS® binder produces coating color compositionshaving essentially the same physical properties as the nondried andredispersed material.

                                      TABLE 15                                    __________________________________________________________________________    Coating and Data for Spray Dried and Redispersed PENGLOSS ® Binder                        Coating Data                                                                  Coating Color                                                                         Coating Color                                                                              IGT.sup.2                                Run No.                                                                            Sample     Viscosity                                                                             Solids  Gloss %                                                                            (cm/sec)                                 __________________________________________________________________________    15A  PENGLOSS ® binder                                                                    1335.sup.1                                                                            63.0    64   46                                            before spray                                                                  drying                                                                   15B  PENGLOSS ® binder                                                                    1280.sup.1                                                                            63.0    66   47                                            after spray                                                                   drying and                                                                    redispersion                                                             __________________________________________________________________________     .sup.1 Model RVF Brookfield Viscometer, Spindle #3, 20 rpm.                   .sup.2 Spring Setting 35 kg, Medium Viscosity oil, Pendulum Drive.       

Example 19

According to this example, coating color compositions were producedcomprising liquid PENGLOSS® binder, spray dried PENGLOSS® binderaccording to Example 18 and liquid reconstituted spray dried PENGLOSS®binder which comprised the spray dried material of Example 18reconstituted in water. The binders were each added to two pigmentsystems with 70% and 76% solids, respectively, and lubricants wereincorporated into some of the coating color compositions.

Clay slips of Nuclay (Englehard) and Hydrasperse (J.M. Huber Corp.) wereprepared at 70% solids by adding the clay to tap water containing0.04-0.05% polyacrylate/NaOH dispersant (commercial solids bases) basedon the clay. Carbital 90, a calcium carbonate (E.C.C. America Inc.) at76% solids was used as received in slurry form.

Coating color compositions were prepared with and without lubricant.Coating color compositions with Nopcote C-104 (Henkel Corp.) used as thelubricant, were pH adjusted to 8.3-8.6 with ammonium hydroxide prior tolubricant addition. Coating color compositions with Berchem 4113 (BercenInc.) used as the lubricant, were pH adjusted with ammonium hydroxide to8.3-8.6 after lubricant addition. All coating colors were thoroughlymixed.

A 28 pound per 3300 square foot unsized, uncalendered, base stock wascoated, calendered and tested with equipment at conditions described inExample 16. Results are shown in Table 16 below. A comparison of Runs16A and 16B shows that the dried and redispersed PENGLOSS® binderproduces a coating color having substantially the same viscosity as thenever dried binder. Runs 16D and 16E illustrate the utility of thebinder at paper coating at high solids levels of 70% whether added as aliquid dispersion (16D) or as dry solids (16E). Runs 16F and 16Gillustrate the utility of the binder for making coating colors withextremely high solids levels of 74%.

                                      TABLE 16                                    __________________________________________________________________________                                     Coating                                                         Lubricant:                                                                             Coating                                                                            Color                                                                              Coat                                                       Type & Amt                                                                             Color                                                                              Viscosity                                                                          Weight                                  Run                                                                              Binder  Coating Color                                                                         (Pts based on                                                                          Solids                                                                             at 20 rpm                                                                          (lb/     IGT.sup.3                      No.                                                                              Compositions                                                                          Compositions                                                                          Clay)    %    (cps)                                                                              side)                                                                             Gloss %                                                                            (cm/sec)                       __________________________________________________________________________    16A                                                                              PENGLOSS ®                                                                        100 parts                                                                             None     63   1170.sup.1                                                                         6.5 64.3 36                                        Nuclay/                                                                       18 parts                                                                      binder                                                             16B                                                                              PENGLOSS ®                                                                        100 parts                                                                             None     63    930.sup.1                                                                         6.9 65.4 39                                (redispersed                                                                          Nuclay/                                                               at 60% solids)                                                                        18 parts                                                                      binder                                                             16C                                                                              PENGLOSS ®                                                                        100 parts                                                                             Nopcote C-104                                                                          63   1140.sup.1                                                                         6.9 66.7 39                                (redispersed                                                                          Nuclay/ 1.0 part                                                      at 60% solids)                                                                        18 parts                                                                      binder                                                             16D                                                                              PENGLOSS ®                                                                        50 parts                                                                              None     70   3700.sup.1                                                                         8.4 62.9 40                                (redispersed                                                                          Carbital 90/                                                          at 60% solids)                                                                        50 parts                                                                      Hydrasperse/                                                                  18 parts                                                                      binder                                                             16E                                                                              PENGLOSS ®                                                                        50 parts                                                                              Nopcote C-104                                                                          70   3910.sup.1                                                                         8.4 63.7 40                                (redispersed                                                                          Carbital 90/                                                                          1.0 part                                                      at 60% solids)                                                                        50 parts                                                                      Hydrasperse/                                                                  18 parts                                                                      binder                                                             16F                                                                              PENGLOSS ®                                                                        100 parts                                                                             None     74   8220.sup.2                                                                         9.5 55.9 42                                (spray dried-                                                                         Carbital 90/                                                          added dry)                                                                            18 parts                                                                      binder                                                             16G                                                                              PENGLOSS ®                                                                        100 parts                                                                             BERCHEM 4113                                                                           74   11000.sup.2                                                                        9.5 56.6 40                                (spray dried-                                                                         Carbital 90/                                                                          0.8 pts                                                       added dry)                                                                            18 parts                                                                      binder                                                             __________________________________________________________________________     .sup.1 Model RVF Brookfield Viscometer, Spindle #4.                           .sup.2 Model RVF Brookfield Viscometer, Spindle #5.                           .sup.3 Medium Viscosity Oil, Pendulum drive, 350 N/cm.                   

Example 20

In this example, a polyvinyl acetate/polyvinyl alcohol film was producedaccording to Example 1 of Columbus, et el., U.S. Pat. No. 3,442,845. Theprocedure of that example was followed using 62.86 grams of polyvinylacetate latex (55% solids, 5,000 cps, nonionic, 3 micron averageparticle size, Unocal 6206, Unocal Corp.); 14.06 grams of polyvinylalcohol (87-89% degree of hydrolysis; medium molecular weight and 23-27cps (4% aq. solution at 20° C.), Airvol 523, Air Products and Chemicals,Inc.), 4.88 grams glycerol (J.T. Baker Chemical Co.); 0.12 gramspreservative (ortho-phenylphenol, Aldrich Chemical Co.); 0.66 gramsdefoamer (Colloid 581, Rhone Poulenc); and 117.22 grams water.

The product mixture was filtered through a No. 100 mesh sieve and drawndown into a film on Mylar film. The film was thoroughly dried at roomtemperature for three days. When the film was subjected to the slidetest of Example 4, the film was very slow to breakup (4-5 minutes) andthen flaked off, slowly becoming thick and soupy as the polyvinylalcohol dissolved. Accordingly, the film was, not considered completelyredispersible, and it was concluded that the coalescable polymerparticles were at least partially coalesced.

Numerous modifications and variations of the above-described inventionare expected to occur to those of skill in the art. Accordingly, onlysuch limitations as appear in the appended claims should be placedthereon.

What is claimed is:
 1. A dried powder capable of being dispersed inwater to form a stable aqueous dispersion comprising at least 20% solidsby weight, said powder comprising a water insoluble component and awater soluble component wherein:(a) the water insoluble componentcomprises coalescable polymer particles which have a T_(g) less than 55°C. and a majority of which have a particle size of less than 1 micron;and (b) the water soluble component comprises a water soluble polymercapable of inhibiting coalescence of said polymer particles, or a watersoluble polymer and a component capable of inhibiting coalescence ofsaid polymer particles; and wherein said coalescable water insolubleparticles comprise greater than 3% and less than 75% by weight of thesolids making up said dried powder and said water soluble componentcomprises greater than about 25% and less than about 97% by weight ofsaid solids.
 2. The dried powder of claim 1 wherein said water solublecomponent comprises greater than 50% by weight of said solids.
 3. Thedried powder of claim 1 wherein at least 90% of said water insolublepolymer particles have a particle size of less than 0.5 microns.
 4. Thedried powder of claim 1 wherein at least 90% of said coalescable waterinsoluble polymer particles have a particle size of less than 0.3microns.
 5. The dried powder of claim 1 wherein said coalescable polymerparticles are prepared from monomers selected from the group consistingof styrene, 1,3-butadiene, vinyl acetate, ethylene, acrylonitrile,acrylic acid, acrylamide, maleic anhydride, monovinyl silicon compounds,ethyl vinyl ether, chlorostyrene vinyl pyridine, vinylidene chloride,butyl vinyl ether, methyl methacrylate, 2-ethylhexyl acrylate, isopreneand chloroprene.
 6. The dried powder of claim 1 wherein said watersoluble polymer is selected from the group consisting of starch,modified starch, starch derivatives, modified starch derivatives,polyvinyl alcohol, cellulose derivatives, polysaccharide gums,polyethylene glycol and maltodextrin.
 7. The dried powder of claim 1wherein said water soluble component comprises a starch hydrolyzateproduct having an intrinsic viscosity less than 0.12 dl/g.
 8. The driedpowder of claim 1 which comprises a crosslinking agent.
 9. The driedpowder of claim 1 wherein said water insoluble component comprisesstyrene-butadiene particles.
 10. The dried powder of claim 9 whereinsaid water soluble component comprises polyvinyl alcohol.
 11. The driedpowder of claim 1 which comprises the reaction product of a thinned,gelatinized starch and unsaturated monomer, said unsaturated monomercomprising at least 10% diene by weight with an unsaturated monomer tostarch ration of between about 2:10 and about 30:10.
 12. The driedpowder of claim 11 which is the product of a persulfate ion initiatedreaction.
 13. The dried powder of claim 12 wherein said diene is1,3-butadiene, a second unsaturated monomer is styrene and wherein saidunsaturated monomer to starch ratio is between about 2:10 and about23:10.
 14. A dried powder capable of being dispersed in water to form astable aqueous dispersion comprising at least 20% solids by weight, saidpowder comprising a water insoluble component and a water solublecomponent wherein:(a) the water insoluble component comprisescoalescable polymer particles which have a T_(g) less than 55° C. and amajority of which have a particle size of less than 1 micron; and (b)the water soluble component comprises a water soluble polymer capable ofinhibiting coalescence of said polymer particles; and wherein saidcoalescable water insoluble particles comprise greater than 3% and lessthan 75% by weight of the solids making up said dried powder and saidwater soluble component comprises greater than about 25% and less thanabout 97% by weight of said solids.
 15. A method of making a dry powdercapable of being dispersed in water to form a stable, aqueous polymericdispersion comprising at least 20% by weight solids, said methodcomprising the steps of:preparing a stable aqueous polymeric dispersioncomprising: (a) a water insoluble component comprising coalescablepolymer particles which have a T_(g) less than 55° C. and a majority ofwhich have a particle size of less than 1 micron; and (b) a watersoluble component comprising a water soluble polymer capable ofinhibiting coalescence of said polymer particles or a water solublepolymer and a component capable of inhibiting coalescence of saidpolymer particles; and wherein said water insoluble particles comprisegreater than 3% and less than 75% by weight of the solids and said watersoluble component comprises greater than about 25% and less than about97% by weight of said solids; drying said dispersion; and forming apowder from said dried dispersion.
 16. The method of claim 15 whereinsaid aqueous dispersion is dried by means selected from the groupconsisting of spray drying, drum drying and vacuum drying.
 17. Themethod of claim 15 wherein the step of drying said dispersion comprisesthe step of selective solvent precipitation.
 18. The method of claim 15wherein said dispersion is prepared by reacting a thinned, gelatinizedstarch and one or more unsaturated monomer(s) comprising at least 10%diene by weight with an unsaturated monomer to starch ratio of betweenabout 2:10 and 30:10.
 19. The method of claim 18 wherein the reaction iscarried out in the presence of a persulfate ion initiator.
 20. Themethod of claim 19 wherein said diene is 1,3-butadiene, a secondunsaturated monomer is styrene and wherein said unsaturated monomer tostarch ratio is between about 2:10 and about 30:10.
 21. A method ofmaking a dry powder capable of being dispersed in water to form astable, aqueous polymeric dispersion comprising at least 20% by weightsolids, said method comprising the steps of:preparing a stable aqueouspolymeric dispersion comprising: (a) a water insoluble componentcomprising coalescable polymer particles which have a T_(g) less than55° C. and a majority of which have a particle size of less than 1micron; and (b) a water soluble component comprising a water solublepolymer capable of inhibiting coalescence of said polymer particles; andwherein said water insoluble particles comprise greater than 3% and lessthan 75% by weight of the solids and said water soluble componentcomprises greater than about 25% and less than about 97% by weight ofsaid solids; drying said dispersion particles; and forming a powder fromsaid dried dispersion.
 22. A dried powder capable of being dispersed inwater to form a stable aqueous polymeric dispersion comprising at least20% by weight solids, produced according to the method comprising thesteps ofpreparing a stable aqueous polymeric dispersion comprising: (a)a water insoluble component comprising coalescable polymer particleswhich have a T_(g) less than 55° C. and a majority of which have aparticle size of less than 1 micron; and (b) a water soluble componentcomprising a water soluble polymer capable of inhibiting coalescence ofsaid polymer particles or a water soluble polymer and a componentcapable of inhibiting coalescence of said polymer particles; and whereinsaid water insoluble particles comprise greater than 3% and less than75% by weight of the solids and said water soluble component comprisesgreater than about 25% and less than about 97% by weight of said solids;drying said dispersion; and forming a powder from said dried dispersion.